This invention relates to calculators and more particularly to calculators having a multiple mode power controller. Multimode power control is a significant advancement over turning off the processor circuitry between keystrokes as described in co-pending application, Ser. No. 106,430, filed Dec. 26, 1979 for "Turn Off Processor Between Key Strokes", by Graham Tubbs, assigned to the same assignee as the present invention. That invention, as does the present invention, addresses the problem of how to minimize power dissipation while maintaining full operational capability. Some calculators, such as that disclosed in the "Turn Off Processor Between Key Strokes" patent application cited above, have essentially three (3) mode systems: off mode, display and processing mode, or display mode. Furthermore, prior calculators system differ from the present invention in that a single main clock oscillator was utilized which was kept on in the display mode, such as described in the above cited co-pending application on "Turn Off Processor Between Key Strokes". Other calculators are essentially two-mode machines, having an off mode and a process and display mode. The main oscillator is always on so long as the calculator is on in the two-mode machine.